Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or a portion thereof with a graphical user interface of one embodiment of our new design.

FIG. 2 is a front view of a display screen or a portion thereof with a graphical user interface of another embodiment of our new design; and,

FIG. 3 is a front view of a display screen or a portion thereof with a graphical user interface of another embodiment of our new design.

The dashed broken line perimeter in the drawings illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines in the drawings illustrate portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described herein. 